An Empirical Formula Predicting Shutdown Dose Rate of the Recirculation Pipes in Boiling Water Reactors

An empirical formula is proposed to estimate the shutdown dose rates around the primary cooling system of boiling water reactors. The formula is characterized by defining the average activation time of ⁶⁰Co, which is proportional to the iron feed rate into the reactor. The constants of the formula are determined by quantitatively evaluating the static balances of corrosion products in the primary coolant on the basis of measured results from the Shimane Nuclear Power Station of Chugoku Electric Power Company. The effects of four radiation reduction procedures on the shutdown dose rate are evaluated using the proposed formula. It is demonstrated that the oxygen injection method is the most effective procedure to reduce the dose rate (to ∼¼). Further reduction (to ∼1/50) can be achieved by a combination of the four procedures.